Adjust the card until it matches a standard bank card placed against the screen (85.60 × 53.98 mm).
Measure distances directly on the screen with horizontal and vertical rulers, a movable crosshair, and live coordinates.
Pixel mode uses browser CSS pixels immediately. Centimeter and inch modes require a quick on-screen calibration against a standard bank card so the ruler can account for display size and system scaling.
Pixel mode measures CSS pixels, the units used by web layouts and browser screenshots. Move the pointer over the ruler to read horizontal and vertical coordinates from the origin.
Browsers do not know the exact physical size of every screen or the effect of system scaling. Calibrating with a real card corrects the physical-unit estimate for the current display and browser setup.
Related tools: Screen Resolution · Refresh Rate Test · Monitor Test